The impact of tracking system properties on the most likely path estimation in proton CT

Proton CT nowadays aims at improving hadron therapy treatment planning by mapping the stopping power of materials. In order to optimize a spatial resolution of the reconstructed images, the most likely path (MLP) of each proton can be computed. We investigated the errors in the computation of this path due to the configuration of the system, i.e. the spatial resolution of the tracking planes, their material budget, and their positioning. A method for computing the uncertainty in the estimated paths for a given system was derived. The uncertainties upon the entrance and exit of the object were propagated analytically in the path computation. This procedure was then used to evaluate the impact of each parameter, and to compare different systems. We show that the intrinsic characteristics of the system generate an uncertainty in the positions and directions of the particles propagated during the MLP computation. The spatial resolution and material budget of the trackers in particular may affect the path estimation, and thus the spatial resolution of an image.